The present disclosure relates to systems and methods for producing high pressure steam using a poor or low quality feedwater source. This can be accomplished without continuously treating large quantities of water.
During combustion, the chemical energy in a fuel is converted to thermal heat inside the furnace of a boiler. The thermal heat is captured through heat-absorbing surfaces in the boiler to produce steam. The fuels used in the furnace include a wide range of solid, liquid, and gaseous substances, including coal, natural gas, and diesel oil.
Steam generation from a boiler system involves thermal and physical processes of heat transfer, fluid flow, evaporation, and condensation of a feedwater fluid mixture that includes water and steam. As the temperatures and pressures of the feedwater and the produced steam change, dissolved materials in the water can precipitate and/or deposit in the waterside of the boiler. These include materials such as oxides, hydroxides, hydrates, carbonates, and other organic/chemical impurities. These deposits can result in the formation of scale on the insides of tube surfaces, or can facilitate corrosion of structural materials within the boiler system. These deposits and/or corrosion combined with the high heat fluxes found in the furnace section of a boiler may lead to tube failures. While scale/deposits can be removed using various maintenance and clean-up processes, this leads to downtime.
Typical systems for supplying high-pressure high-temperature steam to various processes generally involve the direct heating of the feedwater in the boiler. High purity feedwater is typically required to avoid scale/deposits within the tubes of the boiler, other devices associated with the system, and the piping in fluid communication therewith. Low quality feedwater can be treated/cleaned to obtain high purity feedwater. While this is acceptable in a closed loop where the treated high purity feedwater is recycled through the boiler, the treatment/clean-up of the feedwater becomes prohibitively expensive in an open loop cycle because the feedwater treatment system would need to continuously produce high purity water at a rate that is equal to the steam flow requirement of the process. Otherwise, the heat flux in the boiler tubes caused by using low quality feedwater would result in deposits/accumulation of impurities.
However, not all commercial processes that require high-pressure steam also require the steam be at as high a level of purity as the feedwater for a boiler system. It would be desirable to provide systems and methods that can produce high-pressure steam without the concurrent need to continuously produce or use high quality feedwater, and without increasing boiler downtime or maintenance.